1. Field of the Invention
This invention relates to an automatic focus adjustment camera in which the focus deviation relative to the object field is detected to automatically accomplish the focus adjustment of a photo-taking lens.
2. Related Background Art
Generally, in an automatic focus adjustment camera, the focus deviation relative to the object field is detected and the focus adjustment of a photo-taking lens is automatically accomplished on the basis of the detected focus deviation information, and as the processing sequence for this automatic focus control, various propositions have heretofore been made from the relation to the photographing operating by the photographer.
For example, a system for starting the servo control of the photo-taking lens by the first operation of the shutter release button of the camera, for example, the operation of depressing the shutter release button by a first stroke, is widely known, and this system is broadly divided into the so-called one-shot servo system wherein the in-focus state obtained by the servo control of the lens is held until the first operation of the shutter release button is released and the so-called continuous servo system wherein the servo control of the lens is continued so that the lens is focused to the object field as long as the first operation of the shutter release button is continued.
Moreover, the one-shot servo system is an in-focus priority system wherein even if shutter release is attempted by the second operation of the shutter release button, for example, the operation of depressing the shutter release button to a second stroke, the exposure operation by the shutter of the camera is not accomplished unless and after the in-focus state has been obtained by the servo control of the lens, whereas the continuous servo system is usually a release priority system wherein even if the in-focus state is not obtained before the servo control of the lens is completed, the exposure operation can be executed at any time by the operation of the shutter release button to the second stroke.
For example, Japanese Patent Publication No. 41331/1985 proposes an automatic focus adjustment camera provided with the one-shot servo system and the continuous servo system and usable with these two systems changed over by the photographer by means of a mode change-over device.
However, the one-shot servo system and the continuous servo system have their own merits and demerits, and where the change-over system for the two systems is adopted, their respective merits can be effectively availed of, but their demerits are unavoidable.
That is, in the one-shot servo system, it may be mentioned as its merit that unless the in-focus state is obtained, the exposure operation is not effected and therefore photographs which are always in focus can be taken and the first operation of the shutter release button is maintained, whereby the lens can be fixed in the first in-focus position and therefore the focus can be intactly locked and the framing can be easily changed. On the other hand, the demerit of the one-shot servo system is the low traceability of the lens control relative to objects to be photographed which are in vehement motion. That is, once the in-focus state has been obtained, the lens remains stationary unless the first operation of the release button is released and the first operation is again executed. Accordingly, this system is bad in the response of the servo control which responds to the first operation for again obtaining the in-focus state for the movement of the object to be photographed immediately after the in-focus, and the time delay in the meantime causes the shutter chance to be missed.
Also, in the case of the continuous servo system, control of the lens is continued relative to the object to be photographed as long as the first operation of the shutter release button is maintained, and this leads to the merit that photographs which are in focus can be taken at a certain degree of probability and the shutter chance is not missed, but there is the demerit that for an object to be photographed which is in more vehement motion, too much priority is given to the shutter chance and this results in a photograph which is out of focus.
Accordingly, even if a camera is provided with both the one-shot servo system and the continuous servo system and the two systems are made changeable over simply by the photographer's judgement, the demerits of the respective systems will not be eliminated.